Cash-strapped energy bill-payers should give up hot drinks, take showers together and go to bed early in order to cut their energy usage, according to a supplier that raised prices by 18 per cent last year.

First Utility, Britain’s biggest independent energy supplier, which has about 300,000 customers, issued its advice in a “5:2 energy diet” plan that it said would cut £150 from a typical bill.

It suggested consumers reduce their energy usage on two days of each week by following the tips, such as to “opt for an early night”.

“Up to you what you do,” it said, “but putting out the lights and turning off the box can save you £18 a year – and it could be lots of fun…”

The supplier, which raised priced by 18 per cent last summer, advised customers to “shower together”, adding: “Romantic or awkward? Either way sharing a shower can save you £34 a year. Just ask permission from the other person first!”

It also suggested consumers “give up caffeine” as by not boiling a kettle for two days a week they could save about £10 a year.

Playing Monopoly “or any other family game” and reading books instead of watching TV, cooking in bulk and using a clothes airer instead of the tumble dryer were also on the list.

The advice met a chilly reception from Labour’s shadow energy minister Tom Greatrex. “Rising energy bills really aren’t a laughing matter and cause genuine hardship for millions of people,” he said. “Issuing ridiculous advice, however tongue in cheek, will insult and annoy many consumers who are struggling to heat and power their homes this winter.”

Ed Kamm, First Utility’s chief customer officer, defended the advice, saying: “We consistently offer some of the cheapest tariffs on the market and guarantee to be cheaper than the Big Six standard tariffs. But we also want to help our customers use less energy where they can by shedding some light on what different activities cost.

“These tips are meant to provide some advice as to how we might reduce our energy usage and absolutely not intended to trivialise the issue of fuel poverty, something we take very seriously.”

First Utility is known for its outspoken approach to encouraging customers to cut their energy usage